GRAINS-Soybeans firm on export demand, South America weather

* Soybeans rise for three out of four sessions

* Wheat eases after 1-month top; Australia, Argentina assessed

* Corn little changed as market awaits U.S. harvest news

(Updates with European trading, changes byline/dateline) PARIS/SINGAPORE, Sept 18 (Reuters) - Chicago soybean futures rose on Monday for a third session out of the last four, as strong export demand and weather risks for South American planting supported prices. Wheat edged lower as the cereal market faced resistance on price charts after reaching a one-month high on the back of short-covering by investment funds and doubts over harvest prospects in Australia and Argentina. Corn was almost unchanged as investors assessed South American weather concerns while awaiting further clues about U.S. harvest yields. Grain markets will get an update on the U.S. harvest from the U.S. Department of Agriculture's (USDA) weekly crop progress report later on Monday. The Chicago Board of Trade most-active soybean contract added 0.2 percent to $9.70-3/4 a bushel by 1129 GMT. The U.S. Department of Agriculture said on Friday that private exporters sold 132,000 tonnes of U.S. soybeans to China, the latest in a string of export sales. Cash values for soybeans continued to firm at the U.S. Gulf, supported by exporters seeking beans for September loadings. In addition, Argentina's 2017/18 soybean harvest is expected to fall by as much as 7 percent to 52 million tonnes compared with 2016/17, local agriculture analysts said on Friday, citing low profit margins and heavy rain. "Demand is going to be strong and that is a known factor," said one India-based agricultural commodities analyst. "But what is uncertain is the weather. There is talk about La Nina impacting crops in Brazil and Argentina." Dry conditions in Brazil are expected to delay the start of soybean planting in Brazil. However, the U.S. harvest that is getting under way could limit upside to prices if it produces a record crop as projected by the USDA. CBOT wheat eased 0.5 percent to $4.46-3/4 a bushel. It earlier set a new one-month high of $4.50-3/4 but like last week failed to break clear of chart resistance around $4.50. Reduced forecasts for Australia's harvest and heavy rain in Argentina have shifted attention away from large global stockpiles, although big harvests in Black Sea exporters Russia and Ukraine remained a curb.

"Exporters will have to monitor the price evolutions in the Black Sea area while this origin is staying very competitive," consultancy Agritel said in a note. "Nevertheless, the delicate situation in Australia is offering an element of support to international markets." CBOT corn inched down 0.1 percent to $3.54-1/4 a bushel. Private analytics firm Informa Economics, meanwhile, said it expects U.S. farmers in 2018 to devote more acres to corn and wheat and fewer to soybeans, according to an Informa client note.

Prices at 1129 GMT

Last Change Pct End Ytd Pct Move 2016 Move CBOT wheat 446.75 -2.25 -0.50 408.00 9.50 CBOT corn 354.25 -0.50 -0.14 352.00 0.64 CBOT soy 970.75 2.00 0.21 1004.00 -3.31 Paris wheat Dec 163.00 -0.25 -0.15 175.00 -6.86 Paris maize Nov 156.75 -1.00 -0.63 170.00 -7.79 Paris rape Nov 367.50 0.00 0.00 383.25 -4.11 WTI crude oil 49.62 -0.27 -0.54 53.72 -7.63 Euro/dlr 1.20 0.00 0.13

Most active contracts - Wheat, corn and soy US cents/bushel, Paris futures in euros per tonne

(Reporting by Naveen Thukral in Singapore and Gus Trompiz in Paris; Editing by Christian Schmollinger and Adrian Croft)